>I really don't know ??,? there are too many variables here for me to work out.
>We don't have any fitted with Hirth engines so i don't know about the engine,
>the speeds are in MPH and we work in knots (even though Australia is Metric) and
>i have never used or seen a powerfin propeller.? I am going to try and convert
>all your figures and see what i get.
>
>I am also going to post this on the eGroup bulletin board for other owners
>worldwide to have a look at as there may also be another owner out there with
>the Hirth. Finally i have forwarded this to the factory in France, as they have
>more exposure to different configurations.
>
>A big question before we chase ourselves in circles is, how did you set up the
>flaps and ailerons, i have found the wrong flap setting in the "F" will upset it
>considerably !!, it needs to be set up properly to fly at it's best. The other
>thing i have heard about the Hirth's (and don't quote me it is third hand) is
>that the HP figures quoted are not close to the true achievable performance....
>take 5 HP of it ?? i would like to know the answer to that one also
>
>Thanks Michael
>
>"Magrini, William J" wrote:
>
>> Michael,
>> I am running a Hirth 2706 on an Xair-F
>> I have a Powerfin F prop with a 3.16 reduction.? My 68" 3 blade prop is set
>> at 14.5 degrees pitch to give me 6000 RPM at climb and about 6200 max RPM.
>> The plane weighs 256 kilos with 7 gal of fuel and full gross or 450 kilos,
>> with one 210 lb. pilot and a 215 lb. passenger.
>> I calculated the CG as follows:
>> Nose = 13.634 kilos
>> Right = 125 kilos
>> Left = 117.3? kilos
>> 13.334 x 146 = 1991/255.9 = 7.77 cm. Forward of datum.? So my nose is light
>> due to the light engine, but for some reason, my overall weight does not
>> seem light.?? Is that acceptable?
>> My 13 lb. 18 amp battery is behind the seat as far forward as possible. I
>> guess I could get a lighter battery or mount it behind the engine.
>> My speeds are alot higher than Xair specs show.? The plane climbs at about
>> 500 fpm, at about 50 to 55 mph which, I guess is okay for a hot day, and a
>> heavy load.? Cruise is about 60 to 65 mph indicated at 5800 to 6000 RPM.
>> The plane stalls much higher than the 30 mph indicated in the factory specs:
>> about 46-48, no flaps.? The trouble I'm having is that:
>> 1. The flight numbers are higher than indicated by the manufacturer.
>> 2. When I throttle back to 5500, I quickly drop speed to around 55 or so and
>> I loose altitude.? I need about 5800 RPM to maintain level flight, and about
>> 6000 RPM for a slight climb.
>> 3. The engine overheats if I maintain 5800 RPM or better. I mean really hot.
>> 550+ CHT
>> EGTs are O.K. at about 1100.? I have an air dam on the front cylinder (as
>> recommended by Hirth because the plane is in a tractor congiguration) and
>> both cylinders read the same.
>> I talked to Stuart at Powerfin and he says I need more pitch to the prop, in
>> order to be able to have more thrust at lower RPMs.? He says myt static
>> thrust is good, but cruise thrust is probably inadequate to overcome the
>> plane's drag at cruise speed - especially when the plane is fully loaded.
>> He says I'll have to cut the prop from 68" to 66" to allow for more pitch
>> and allow the engine to develop full power. The Hirth 2706 is rated at 65 hp
>> at 6200 RPM.? Maximum torque is at 5700 RPM.? So the engine runs at a lower
>> RPM than the Rotax 582.? I asked Stuart if he thought I needed a lower ratio
>> gear box (like 2.59) and he said he didn't think that would help.
>> Questions:
>>???????? How does this compare with your 2 seat performance on the Xair at
>> gross weight using a Rotax 582 engine?? I know you like the 618, but how
>> does the 582 perform at Gross?
>>???????? Do you think the prop is running too slow because of the 3.16 gear
>> ratio? What ratio do you run with the 582. What prop pitch.
>>???????? What are your recommendations?? (I can't afford a 618 right now.)
>
>
>------------------------------------------------------------------------
>CLICK HERE AND START SAVING ON LONG DISTANCE BILLS TODAY!
>
>------------------------------------------------------------------------
>
>
>
>
>
>